Adric creates a diversion, allowing for the Doctor to escape from the police and them both to run into the Tardis. Finding themselves trapped by the Master the Doctor jettisons Romana's room to create extra thrust. The Doctor believes the Master is still in the Tardis and decides to flush him out by materialising under water in the Thames. However the Tardis instead materialises on a barge! Going outside the Doctor sees the Watcher again and speaks with him, returning gravely worried. He & Adric set course for Logopolis, resuming their earlier plan to repair the chameleon circuit. However after they leave Tegan stumbles into the console room. They reach Logopolis where it's leader, the Monitor, greets his old friend and arranged for the Logopolitans to make the necessary calculations for the Block Transfer Computations to be based on. The Master kills one of the Logopolitans and introduces an inaccuracy into the chanted computations. The Doctor recognises the central register on Logopolis as a replica of the Pharos project on Earth. The Doctor tests his Tardis, as Adric encounters Nyssa who has been brought to Logopolis by a friend of the Doctor seeking his his help to find her missing father. As the Doctor runs his test, observed by his companions, the Logopolitans and the Watcher, instead of changing shape the Tardis starts to shrink with the Doctor trapped inside......

How barking mad is the Doctor's plan to literally "flush" the Master out of the Tardis? He'll open the doors and wash him out? Along with all the other junk he's accumulated that'll make for a Thames suddenly full of rubbish. He's not even sure the Master is still there, the idea seems to suddenly occur to him as Adric says flush and he just runs with it without thinking. Deary me. It sticks out like a sore thumb as particularly barking. we do get a good demonstration of what the Doctor is trying to fix as the Master's Tardis demonstrates it's chameleon circuit changing from a Police Box to a Bush to an Ionic Column.

The locations in this episode are very adjacent to each Cadogan Pier and Albert Bridge. Towards the end of the sequence the four chimneys of Battersea Power Station are clearly visible in one shot while the two chimney station seen is Lots Road Power station which for many years provided the power for the London Underground. It's close to both the fictional location for the Tardis landing in Dalek Invasion of Earth, which shows a ruined Battersea Power Station, and the actual location used for the Dalek's emergence from the Thames in the film version of the same story. The location in the original story is found further west at Queen's Wharf in Hammersmith.